Coating compositions



g the greening effect.

- to greening.

Patented Apr. 3, 1945 UNITED STATES PATENT OFFICE COATING COMPOSITIONS Ernest G. Almy, Tamaqua, Pa., assignor to Atlas Powder Company, Wilmington,

tion of Delaware Del., a corpora- No Drawing. Application October 18 1940,

a Serial No. 361,719

4 Claims.

The present invention relates to improvements in coating compositions. More particularly it relates 'to coating compositions which are resistant to the greening action likely to occur when bronze or brass hardware are frequently coated with a clear lacquer to improve their lustre and prevent tarnishing. Where small articles are to be coated it is economical to dip them into a relatively large body of lacquer. Another way of coating small articles is to spray themunder con- 4 ditions in which the excess lacquer is recovered and reused. In these and other known processes, it happens that a relatively large and valuable quantity of lacquer must be used and repeatedly contacted with the copper-containing articles. Under these circumstances the lacquers are often rendered useless by the development therein of a green or blue-green coloration probably attributable to the formation of copper compounds with the constituents of the lacquer or with decomposition products of the lacquer which are always present in greater or lesser amounts. large body of clear hardware lacquer develops this foreign coloration it is of no further use for the purpose and must be discarded.

Heretofore malic acid has been proposed as an anti-greening agent.for clear coating compositions to solve the problem described above. When incorporated into the composition in small proportions, malic acid substantially decreases However, malic acid is objectionable in that the coatings produced from compositions containing malic acid tend to "bloom." The malic acid tends to crystallize out of the coating, particularly after extremevariations in atmospheric conditions. This produces the cloudy eifect known as bloom" and in extreme instances a white deposit of malic acid is formed on the surface of the coating.

An object of the present invention is to provide coating compositions which are highly resistant Preferably I employ monoethyl mal compatible with coating compositions of resin or cellulose derivative base and are soluble in the ordinary lacquer solvent mixtures. The esters are generally superior to straight malic acid in imparting greening resistance to the composition and to the coating produced therefrom. While with some coating compositions the greening effect cannot be entirely eliminated, in each instance the greening is inhibited by these esters When a will hereinafter to agreater extent than where free malic acid is employed in equivalent proportion.

Moreover, the coatings containing these esters are free from any observable tendency to bloom." Even under accelerated test conditions wherein articles coated with my improved lacquer were submitted to alternate high and low humidities no bloom" developed. Under similar tests coatings containing malic acid became cloudy and crystals of malic acid deposited on the surface of the coating.

It has previously been proposed to use certain malate esters in connection with the problem of the livering or gelling oi pigmented nitrocellulose lacquers. Thus, the patent to Burke, No. 2,026,- 493, describes incorporating ethyl malate in a bronzing lacquer to prevent gelling. The lacquer described in this patent contains a high percentage of bronzing powder as a pigment and the problem to be solved is said to be to keep the lacquer from becoming solid after the bronze powder'is incorporated. This is an entirely different problem than the one solved by the present invention which deals entirely with clear lacquers and preventing the development of an undesirable color in them.

Non-limiti g examples of the preparation of the greening inhibitors of the present invention are as follows:

EXAMPLE 1 An alcoholic solution of monoethyl malate was prepared by boiling undera reflux condenser a mixture of 30 g. malic acid with su'flicient denatured alcohol to make a volume of ml. Heating was continued for about 17% hours, at which time the ratio of saponification number to acid number had risen to about 2, the theoretical value for the mono ester.'-

EXAMPLE 2 Monohexyl malate was prepared by heating hexyl alcohol with malic acid in equimolecular monoester of malic acid is added to a clear uer of a type suitable for use in coating copper= containing articles. Such lacquers are generally of cellulose ester or ether, or of the resin base which may be used include both natural and syn thetic resins of the types well known in the varnish and lacquer art. Thus, among natural resins are damar, elemi and the like and mad aeration 5% ethyl alcohol solution of mono-beryl malato (prepared in Example 2) in place of the mono= ethyl malate oi Erample 3.

natural resins like ester gum. Synthetic such as alkyd and phenol-aldehyde resins, oil modified synthetic resins and many others can be employed. In general the composition of the present invention can be said to comprise e. of clear, film-forming resin or cellulose ester or ether. a

As a rule the coating compositions are made no of mixed bases and other added materials like plasticizers. The composition comprises a sol vent or mixture of solvents of the usual typm.

It will be understood that the invention will be employed only with clear coating compositions in connection with which there is a greening problem and which, furthermore, are benefited by the inclusion of an allryl mono-ester of malic acid.

There are some types of compositions whichare so corrosive that even an ester of malic acid will not prevent greening. Most of the coat-= ing compositionssubiect to greening, however, will be found to be substantially improved or cured of this defect by treatment according to my invention.

Non-limiting examples of coating compositions of the present invention areas follows:

EXAMPLE 3 Per cent Butyl acetate so Pent acetate (commercial amyl acetate) lb Butyl a1cohol i i Ethyl alcohol ll Toluol 5 Xylol' 5 Damar solution (6 lbs. resin/gal. Solvent A) l5 Rezyl resin solution (oxidizing type (oilmodiiied alkyd resin produced by American Cy= r anamid 8; Chemical Corp.) 6 lbs. resin/gal;

toluol) 5 Shellac solution (6 lbs. shellac/gal. alcohol) 2 ice l25-centipoises nitrocellulose 5 eta/gal. of above 6-second nitrocel1ulose l oz./gal. of above Solvent A. 1

Per cent Ethyl acetate 2b 'Low boiling petroleum naphtha 3b .Ethyl alcohol (SD #1) 5o This lacquer has added thereto 2% byvolume of anethyl alcohol solution containing the equivalent of 2 5 g. malic acid per 100 ml. solution- (30.25 g. mono-ethyl malate per 100 ml. solution).

. The. lacquer shows excellent anti-greening 76 properties and is not subject to bloom.

EXAMPLE 4 All The resulting lacquer is free from tendency to green and also is not subject to bloom.

The other greening inhibitors of the invention can be substituted in place of the ones used in the examples. Various other lacquer iorrnula= tions can be improved as to resistance to greening by the addition'oi the inhibitors or the inven tion. it will be understood that the invention is not limited to the proportions of greening inhibi tors set out in the examples but that wide varia= tion is permissible. The proportion will usually be unite small, just sumcient to accomplish the desired result. in most instances it is not desire ble to use more than 3 or 4% of the allryl malate based on the lacquer, and 1% or less will usuady be preferred.

in the claims which follow I have used the clear referring to my composition to distin= guish it from pigmented compositions. i do not, however, intend toexclude colored compositions where the color is produced by conventional means other than pigments.

The term allryl monoester of malic acid denotes a mixture oi the two isomeric monoesters, obtain= able by a non-specific reaction such as is illustrated in. Examples 1 and 2.

The invention is to be taken as limited only by the scope of the following claims:

l. The method. for making a clear hardware lacquer for use in coating copper-containing al articles by processes such as dipping in which (ill a body of the lacquer is repeatedly brovgh contact with successive articles of said 9,3, whereby said lacquer tends to develop an unclesirable green color, which comprises adding to a lacquer, comprising nitrocellulose, moncethyi malate in an amount not over about 4%, based on the lacquer, as a greening inhibitor.

2. A clear hardware lacquer ior use in coating copper-=containing metal articles by processes such as dipping in which a body of the lacquer is repeatedly brought into contact with successive articles oi said metal whereby it tends to acquire an undesirable green color, which lacquer corn prises a clear, iilm-forming base, comprising ni-= trocellulose, and monoethyl malate in an amount not over about l%,, based on the lacquer, as a greening inhibitor.

3. The method for making a clear hardware lacquer for use in coating copper-containing met al articles by processes such as dipping in which a body or the lacquer is repeatedly brought into contact with successive articles of said metal whereby said lacquer tends to develop an undesirable green color, which comprises adding to the lacquer an alkyl monoester of malic acid, in which the alkyl group contains from 1 to 7 carbon atoms, in an amount not over about 4%,

based on the lacquer, as a greening inhibitor.

t. A clear hardware lacquer for use in coating copper-containing metal articles by processes such as dipping in which a, body of'the lacquer is repeatedly brought into contact with succes sive articles of said metal wherebylt tends to acquire an undesirable green color, which'lacquer comprises a clear film-forming, base and an al-l kyl monoester of malic acid, in which the allryl group contains from 1 to 7 carbon atoms, in arr amount not over about 4%, based on the lacquer; as a greening inhibitor.

ERNET G. 

